Question

A beam of monochromatic light is incident on one face of an equilateral prism. The angle of incidence is $55{}^{\circ }$ . If the angle of emergence is $46{}^{\circ }$ , then the angle of minimum deviation ${\delta }_m$ will be

• A. $>41{}^{\circ }$
• B. $<41{}^{\circ }$
• C. $=41{}^{\circ }$
• D. $\ge 41{}^{\circ }$

Answer 1

Answer: (B)

Given $A=60{}^{\circ }$ $e=46{}^{\circ }\Rightarrow i=55{}^{\circ }$ Since, $i+e=A+\delta$ $\Rightarrow$ $55+46=60+\delta$ $\Rightarrow$ $\delta =41{}^{\circ }$ Practically the angle of minimum deviation for a glass prism is less than $40{}^{\circ }$ (about $38{}^{\circ }$ or $39{}^{\circ }$ ) So, $\delta <41{}^{\circ }$